When a new voter registers in Colorado, the secretary of state mails a nonforwardable notice of disposition that the voter’s registration has been received. If the notice comes back undeliverable in the mail, then clerks deem the voter’s registration inactive within 20 days.
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The motion for the preliminary injunction is one of several federal challenges regarding purged voters filed against the secretary of state by Common Cause of Colorado, Mi Familia Vota Education Fund and the Service Employees International Union

You have to submit ID if you’re buying a beer or riding an Amtrak train, but you can vote without ID. Does that make any sense?